Use of parvovirus for eliminating cancer stem cells (CSCs)

ABSTRACT

Described is the use of a parvovirus, preferably H-1PV, for the therapeutical elimination of cancer stem cells (CSCs), preferably neuroblastoma stem cells and glioblastoma stem cells.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 13/807,736filed on Dec. 30, 2012, which in turn is a U.S. national phase under theprovisions of 35 U.S.C. § 371 of International Patent Application No.PCT/EP11/03197 filed Jun. 29, 2011, which in turn claims priority ofEuropean Patent Application No. 10007007.7 filed Jul. 7, 2010. Thedisclosures of such U.S. application, international patent applicationand European priority patent application are hereby incorporated hereinby reference in their respective entireties, for all purposes.

The present invention relates to the use of a parvovirus, preferablyH-1PV for the therapeutical elimination of cancer stem cells (CSCs),preferably neuroblastoma or glioblastoma stem cells.

In children, tumors originating from the nervous system are the mostfrequent solid tumors. Among them, neuroblastoma is the most frequentextra cranial solid tumor. It is derived from progenitor cells of thesympathetic nervous system resulting in highly malignant tumors alongthe sympathetic chain. High risk neuroblastoma is frequentlycharacterized by a MYCN oncogene amplification and consecutiveoverexpression of the N-myc Protein. Despite the introduction ofmultimodal treatment concepts including surgery, radiopharmaceuticaltreatment by metaiodobenzylguanidine, high-dose chemotherapy withautologous stem cell rescue, local irradiation and retinoic acidmaintenance therapy high risk neuroblastoma patients have an extremelypoor outcome with long term survival rates of about 30%. These tumorsremain a therapeutic challenge and surviving children suffer fromtreatment related acute and long term toxicities.

Malignant human glioblastomas account for the largest number of humanmalignant brain tumors. The conventional approaches to treatment ofgliomas include neurosurgical techniques (resection or stereotacticprocedures), radiation therapy and chemotherapy. Radiation therapy (RT)of malignant gliomas increases the survival of patients by severalmonths but, like other standard therapies, it is unable to prevent tumorrecurrence. However, despite these therapies glioblastomas areconsidered as incurable, since treatment with ionizing radiation,chemotherapy and/or surgical resection achieves only a very limitedprolongation of life span of patients. Typically, the average life spanafter diagnosis is on the order of about 12 to 16 months. Therefore,novel treatment modalities, in particular for neuroblastoma andglioblastoma, are urgently required.

Thus, it is the object of the present invention to provide means forefficient therapy of tumors, preferably neuroblastoma or glioblastoma,which overcome the disadvantages of the current therapies.

According to the invention this is achieved by the subject mattersdefined in the claims. It was surprisingly found that parvoviruses canbe successfully used for efficient therapy by killing of cancer stemcells.

Oncolytic viruses are a promising novel class of cancer cell-specificbiological agents, infecting and killing transformed cells while sparingnormal tissues. In addition to the oncolytic effect observed both invitro and in vivo, these viruses also provide immunostimulatory signalsinducing the elimination of virus-infected tumor cells. Thereby theinnate and adaptive immune systems gain access to tumor antigens, whichresults in cross-priming and vaccination effects. In neuroblastomamodels, a variety of genetically engineered oncolytic viruses have beenapplied including Newcastle disease virus, attenuated poliovirus, andoncolytic herpes simplex virus 1 and 2.

Some autonomous rodent parvoviruses were shown to preferentially killtransformed and tumor-derived rodent and human cell lines in vitro,while no cytocidal action was observed in non-transformed cells. Inparticular, H-1PV was found to replicate and exert cytopathic effects ina variety of transformed or tumor derived cells, whereas non-transformedcells remain unaffected in vitro and in vivo. The oncolytic effects ofH-1PV observed have been attributed to different cellular deathprograms, including apoptosis, necrosis of the infected cells orlysosomal membrane permeabilization which causes the release ofcathepsins from the lysosomal lumen to the cytosol. The individualmechanism by inducing cellular death in different malignacies seems todepend mainly on the individual cellular background.

H-1PV is a small (20-25 nm), non-enveloped parvovirus containing alinear single-stranded DNA genome of about 5 kb. Its replication in thenucleus is strictly dependent on S-phase-associated factors and thecompletion of the lytic infectious cycle is tightly dependent oncellular factors that are expressed as a consequence of proliferationand differentiation processes. The non-structural protein NS1 plays anessential role in initiating the parvoviral replication and in inducingits cytotoxicity. Parvoviruses are incapable of inducing quiescent cellsto enter S phase, and infection remains cryptic until the host cellsenter DNA replication on their own. This dependency on the replicationof the host cells accounts, in part, for the tissue specificity,oncotropism, and oncolytic activity of autonomous rodent parvoviruses.

Rats are the natural host of H-1PV, but other rodents such as hamsterand mastomys could be experimentally infected. Occasionally, theinfection and seroconversion of humans has been reported. H1-PV appearsto be non-toxic in humans, even when applied systemically. The oncolyticeffects of H-1PV have been studied in vitro and in vivo on a variety ofhuman entities such as lymphoma, pancreatic cancer, glioblastoma celllines, hepatoma, and breast cancer. However, the oncolytic effect ofH-1PV on pediatric tumors had not been studied so far.

In the studies resulting in the present invention a pre-clinical invitro assessment of the application of oncolytic H-1PV for the treatmentof neuroblastoma cells was performed. Infection efficiency, viralreplication, and lytic activity of H-1PV were analyzed in elevenneuroblastoma cell lines with different MYCN status. Oncoselectivity ofthe virus was confirmed by the infection of short term cultures ofnon-malignant infant cells of different origin. Mixed culture of gliacells, neuronal cells, astrocytes in short term culture revealed noeffect of H-1PV on viability or morphology of the cells. In contrast, alytic infection was induced in all neuroblastoma cell lines examined atMOIs between 0.001 and 1 pfu/cell. H-1PV actively replicated with virustitres increasing up to 10.000-fold within 48 to 96 hours afterinfection. The lytic effect of H-1PV was observed independent of MYCNoncogene amplification or differentiation status. Moreover, theexpression of viral proteins in a MYCN amplified neuroblastoma cell linecorrelated with down-regulation of N-myc expression. Infectionefficiency, rapid virus replication and exhaustive lytic effects onneuroblastoma cells together with the low toxicity of H-1PV fornon-transformed cells, render this parvovirus a promising candidate foroncolytic virotherapy of neuroblastoma.

In summary, the experiments resulting in the present invention show thatinfection of cancer stem cells, e.g., neuroblastoma stem cells, withparvovirus represents a new and highly effective therapy with only verylow side effects. This kind of therapy is even effective regarding CSCsthat are resistant to chemotherapy and radiotherapy.

Thus, the present invention provides a parvovirus, preferably a rodentparovirus for use in a method for therapeutically destroying cancer stemcells (CSCs).

The term “cancer stem cells (CSCs)” as used herein refers to cancercells (found within tumors or hematological cancers) that possesscharacteristics associated with normal stem cells, specifically theability to give rise to all cell types found in a particular cancersample. CSCs are therefore tumorigenic (tumor-forming), at much lowercell numbers than commonly used cell cultures grown in FCS containingmedium. CSCs may generate tumors through the stem cell processes ofself-renewal and differentiation into multiple cell types. In the morerecent literature the initial term “cancer stem cells” has been replacedby the terms “tumor stem-like cells” or “tumor initiating cells”. Thus,the terms “tumor stem-like cells” or “tumor initiating cells” areessentially synonymous to the term “cancer stem cells”.

This subfraction of malignant cells within a tumor is characterized bythe expression of stem cell markers, such as CD133, nestin and SOX2 fortumor initiating cells of neuroectodermal origin such as glioblastoma orneuroblastoma. For several malignant diseases, among them glioblastoma,it has been shown in vitro and in vivo that conventional cytostatic drugtreatment increases the number of cells within this fraction. Therefore,these tumor stem cells have been hypothesized to cause relapse andmetastasis by giving rise to new tumors. Therefore, the therapy of thepresent invention targeted at CSCs improves survival and quality of lifeof cancer patients, especially for children and for patients withmetastatic disease.

The term “therapeutically destroying cancer stem cells” means that theCSCs are killed by the oncolytic and cytotoxic activity of theparvovirus so that the proportion of CSCs within a tumor decreases withthe treatment.

The term “parvovirus” as used herein comprises wild-type or recombinantderivatives thereof as well as related viruses or vectors based an suchviruses or derivatives. Suitable parvoviruses, derivatives etc. whichare useful for gene therapy are known to the person skilled in the art.

In a preferred embodiment of the use of the present invention the CSCsare (a) cancer stem cells resistant to chemotherapy or radiotherapy, or(b) potentially relapsing cancer stem cells.

In a further preferred embodiment of the use of the present invention,said cancer stem cells are neuroblastoma stem cells or glioblastoma stemcells, which represent a model for cancer stem cells of neuroectodermalorigin.

In a further preferred embodiment, the parvovirus is a rodentparvovirus, preferably H1, or a related rodent parvovirus such as LuIII,Mouse minute virus (MMV), Mouse parvovirus (MPV), Rat minute virus(RMV), Rat parvovirus (RPV) or Rat virus (RV).

For administration these parvoviruses etc. are preferably combined withsuitable pharmaceutical carriers. Examples of suitable pharmaceuticalcarriers are well known in the art and include phosphate buffered salinesolutions, water, emulsions, such as oil/water emulsions, various typesof wetting agents, sterile solutions etc. Moreover, in a metastatic rathepatoma model, H-1 PV could be shown to act as a therapeutic vaccinewhen being delivered in autologous tumor cells serving as carriers(Raykov et al., 2007). Such carriers can be formulated by conventionalmethods and can be administered to the subject at a suitable dose.Administration of the suitable compositions may be effected by differentways, e.g. by intravenous, intraperetoneal, subcutaneous, intramuscular,topical or intradermal administration. If infectious virus particles areused which have the capacity to penetrate through the blood-brainbarrier, treatment could be performed or at least initiated byintravenous injection of, e.g., H-1 virus. However, long termintravenous treatment could become inefficient by the formation ofneutralizing antibodies to H1 virus. Therefore, different modes ofintracranial or intratumoral virus application might be preferable.Moreover, after placement of a silicon catheter connected to a smallsubcutaneous reservoir (Rickham reservoir) during tumor removal or by aseparate procedure, parvovirus can be injected locally at various timeswithout further surgery. The parvovirus or derived vectors can also beinjected into the CSCs with stereotactic surgery or by targeting withneuronavigation. Combinations of the above mentioned methods ofapplication are also possible.

The dosage regimen will be determined by the attending physician andother clinical factors. As is well known in the medical arts, dosagesfor any one patient depend on many factors, including the patient'ssize, body surface area, age, sex, the particular virus, cell etc. to beadministered, time and route of administration, general health and otherdrugs or therapies being applied concurrently.

FIGURE LEGENDS

FIG. 1:

(A) NB124, 72 h after infection with MOI 1 H-1EGFP.

(B) NCH 421, 36 h after infection with MOI 50 H-1EGFP.

(C) Kelly, 48 h after infection with MOI 1 H-1EGFP.

(D) IMR-32, 48 h after infection with MOI 1 H-1EGFP.

FIG. 2:

(A) NS1 Western Blot of NB 124 neuroblastoma progenitor cells.

(B) NS1 Western Blot of three glioblastoma stem-like cells.

FIG. 3: Infection of neuroblastoma initiating cells and glioblastomastem-like cells with wtH-1PV

See Example 4 for details.

FIG. 4:

(A) Cytomorphology of NB 124, three weeks after infection with wtH-1PV.

(B) Cytomorphology of NCH 421, three weeks after infection with wtH-1PV.

FIG. 5: H-1PV infection significantly reduces cell viability inneuroblastoma initiating and glioblastoma stem-like cells within 15 daysafter infection

left panel: MTT NB 124 day 15 after infection with H-1PV

right panel: MTT NCH 421 day 15 after infection with H-1PV

FIG. 6: H-1PV induces cytostatic effects on neuroblastoma initiatingcells and on three glioblastoma stem-like cell lines in a dose-dependentmanner

See Example 7 for details.

The below examples explain the invention in more detail.

EXAMPLE 1 Materials and Methods

(A) Cell Culture

The human neuroblastoma neurosphere culture NB124 was obtained from Dr.Hedwig E. Deubzer (Clinical Cooperation Unti Pediatric Onocology, GermanCancer Research Center). The human glioma stem-like cell lines NCH 421,NCH 441, NCH 620, and NCH 644 were obtained from PD Dr. ChristelHerold-Mende from the Department of Neurosurgery (Campos et al., 2010).Basis medium (for stem cells): DMEM (Sigma Aldrich, Munich), 1%penicillin-streptomycin, 1% L-glutamine. Stem cell medium: Basis medium,20% BIT 100 supplement (provitro GmbH, Berlin), 0.02% bFGF (RELIA TechGmbH, Wolfenbüttel), 0.02% EGF (RELIA Tech GmbH). Trypsin-blockingmedium: DMEM (Sigma Aldrich, Munich), 10% heat-inactivated foetal bovineserum, 1% penicillin-streptomycin. Stem-like cells were grown asneurosphere cultures as previously published and cultured at 37° C., 5%CO₂ in the respective growth medium (Wan et al., 2010).

(B) Virus Production and Infection

Wild-type H-1PV was produced by infecting NB K-324K human embryonickidney cells, and purified by filtration (maximal diameter of particles0.2 μm) and iodixanol gradient centrifugation. The contamination ofvirus stocks with endotoxins was <2.5 EU/ml. Cells were infected withH-1PV as single cell suspensions after typsin treatment in theirrespective growth medium at 37° C.

(C) Detection of Infectious H-1PV Particles

Virus titres were determined as described previously (Angelova et al.,2009). Briefly, NB-324K cells (7.6×10³ cells/well) were seeded in96-well plates 24 h prior to the assay. Cells were infected by 10-foldserial dilutions of the supernatant of the previously infectedneurosphere cultures and incubated for 72 h at 37° C., 5% CO₂.

After alkaline lysis (0.75 M NaOH), DNA was transferred to a nylonmembrane, cross-linked, and hybridized with a NS-1 specific proberadiolabeled with P³². Blots were exposed to X-ray film forautoradiography. Titration experiments were always performed induplicates. Virus was applied at multiplicities of infection (MOI,expressed in plaque-forming units per cell; pfu) as indicated in thetext.

(D) Viral DNA Extraction and Quantitative Real-time PCR

The supernatant of the infected neurosphere cell cultures was collectedat different time points after infection. The supernatant was subjectedto alkaline lysis in 1 M NaOH in TE buffer for 30 min at 56° C. Afterneutralization with an equimolar concentration of HCl the samples werediluted 1:100 with sterile water and directly analyzed. Quantificationof viral DNA was carried out by real-time qPCR with an NS1-specificTAQMAN® dual labeled hydrolysis probe (Applied Biosystems by LifeTechnologies, Carlsbad (Calif.), U.S.A), using an ABI® PRISM® 7700sequence detection system thermal cycler (Applied Biosystems by LifeTechnologies, Carlsbad (Calif.), U.S.A) and analyzed by means of SDS 2.1software (Applied Biosystems by Life Technologies, Carlsbad (Calif.),U.S.A) as described elsewhere (Abschuetz et al., 2006). Briefly, a DNAfragment of 141 nt within the NS1 gene of H-1PV was amplified, anddetected using probe: 5′-6-FAM-ATGCAGCCAG-ACAGTTA-Q-MGB 3′. A plasmidthat contained the NS1-sequence in serial dilutions in the range of10¹-10⁸ copies/reaction was used to standardize the qPCR. Individualreaction mixtures (20 μl) consisted of 1× TAQMAN® Universal PCR MasterMix formulation for real-time PCR (Applied Biosystems), 0.3 μM labelledNS1-TAQMAN® dual labeled hydrolysis probe, 0.3 μM of each primer and 3μl template. PCR conditions were 2 minutes at 50° C. (destruction ofcontaminating template by AMPERASE™ Uracil N-Glycosylase), then 10minutes 95° C., followed by 40 cycles of denaturation at 95° C. for 15seconds and annealing/extension at 60° C. for 60 s.

(E) Microscopy

Phase contrast images were generated using an inverted phase contrastmicroscope (Olympus; Model CKX41) using Cell B software (Olympus EuropaGmbH, Hamburg, Germany). Other phase contrast images were obtained usinga Leica DFC350 FX™ camera (Leica Microsystems, Wetzlar, Germany) and theLeica FIRECAM™ digital image management software for MACINTOSH® digitalcomputers.

(F) Assessment of Cell Viability and Lysis

Proliferation of neuroblastoma cells was tested with the3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assayas recommended by the manufacturer (Sigma-Aldrich, St. Louis, Mo.,U.S.A.). Cells (2,500 cells per well) were cultured in 96-well platesand infected at MOIs indicated in the Figures. After 15 days, cells werewashed in PBS and incubated with 0.5 μg/ml MTT-solution for up to 2hours. After discarding the supernatant and drying the cells, 100 μlisopropanol per well were added. Extinction values were photometricallydetermined at 570 nm (MULTISKAN PLUS™ microplate reader, TitertekInstruments Inc., Huntsville, Ala., U.S.A).

Cell lysis was determined by measuring the release of lactatedehydrogenase into culture medium by use of the CYTOTOX 96® Cytotox 96cytotoxicity assay Kit™ (Promega Corporation, Madison Wis., U.S.A.))according to the manufacturer's instructions.

EXAMPLE 2 Neuroblastoma Progenitor and Glioblastoma Stem-like Cells areSusceptible to H-1PV Infection

To determine if H-1PV was able to infect neuroblastoma progenitor cells,NB124 cells were subjected to one replication unit per cell ofrecombinant, replication-deficient H-1 virus (H-1EGFP) virus expressingGFP. NCH 421 glioblastoma neurospheres were infected with MOI 50 ofH-1EGFP. The MYCN amplified neuroblastoma cell lines Kelly and IMR-32were kindly provided by Prof. Dr. Olaf Witt, CCU Pediatric Oncology,German Cancer Research Center, Heidelberg and served as positivecontrols Immunofluorescence microscopy revealed that GFP expressioncould be detected in both neuroblastoma cell lines and the NB124neurosphere culture and after infection with H-1EGFP, indicatingsuccessful infection of neuroblastoma cells and gene expression drivenby the viral promoter in the neuroblastoma progenitor cells infected(FIG. 1, left panel, phase contrast microscopy, middle panel merge,right panel, fluorescence microscopy).

EXAMPLE 3 H-1PV Protein Expression Persists in Neuroblastoma ProgenitorCells and High Grade Glioma Stem Cells up to 15 Days

In order to demonstrate that the proteins of wtH-1PV were expressed ininfected neuroblastoma and high grade glioma progenitor cells, Westernblot analysis of NS1 and NS2 proteins in infected cells was performed.NS1 and NS2 are non-structural proteins required for infection of hostcells, and VP1/2 are structural viral capsid proteins (Chen et al.,1989; Caillet-Fauquet et al., 1990, Brandenburger et al., 1990).Following infection with 50 pfu per cell wtH-1PV, these viral proteinswere expressed in all stem cell lines investigated, at day 9 and day 15after infection (FIGS. 2A,B). Human neuroblastoma (IMR-32) andglioblastoma (U87) non-stem cell like cell lines served as positivecontrols. U87 human glioblastoma cells grown under standard conditionsserved as positive control.

EXAMPLE 4 H-1PV Actively Replicates in Neuroblastoma Progenitor Cellsand Glioblastoma Stem-like Cells

In order to address the issue whether H-1PV was able to multiply inneuroblastoma progenitor cells, cells were infected with wtH-1PV. Viralgenome copy numbers in the supernatant were determined by real-time PCRin a time period ranging from 3 days up to 21 days after infection. InNB 124 neuroblastoma cells, the viral genome copy numbers increased upto 1,000 fold and the titer of infectious particles even increased up to100,000 fold indicating highly efficient viral multiplication in thesecells. The efficiency of replication of fully infectious viral progenyin these neuroblastoma progenitor cells even exceeded that observed instandard neuroblastoma cell lines which displayed a significant increasein viral copy numbers varying from a 10² to 10⁴ fold increase within 72to 144 h after infection (Lacroix et al., 2010).

In NCH 421 glioblastoma stem-like cells viral genome copy numbersincreased up to 10,000 fold during 21 days after infection, which iscomparable to the replication efficiency in other human glioma celllines without stem-cell properties (Geletneky et al., 2005).

In order to quantify the generation of infectious progeny H-1PV,infectious particle assays with supernatants of the same infectedneuroblastoma progenitor cell line in culture were additionallyperformed. The progeny H-1 viruses were biologically active, i.e. ableto infect NBK-324K cells. In the infection unit assay, a 4,000-foldincrease in the neuroblastoma neurosphere culture NB124 and a 3,500-foldincrease of infectious particles in the glioma stem-like cell line NCH421 compared to the input virus could be determined (FIG. 3; uppercurve: Vg/ml; lower curve: IU/ml).

Taken together, H-1PV could be proven to productively infectneuroblastoma progenitor cells and glioblastoma stem-like cells.Infection of these cells could be demonstrated to induce the expressionof essential viral proteins, efficient viral replication and productionof infectious H-1PV progeny.

EXAMPLE 5 H-1PV Induces Lytic Infection in Neuroblastoma and High GradeGlioma “Stem” Cell Lines

In order to test to what extent infection of neuroblastoma cells withwild type H-1PV was lytic, the cytomorphology of the infected cells wasdocumented by phase contrast microscopy. Three weeks after infectionH-1PV could be shown to induce significant cytopathic effects oncultured NB124 cells applying an MOI of 0.01 p. f. u. per cell or more(FIG. 4A). Three weeks after infection H-1PV could be shown to inducesignificant cytopathic effects on cultured NCH 421 cells applying an MOIof 1 p. f. u. per cell or more (FIG. 4B).

EXAMPLE 6 H-1PV Infection Significantly Reduces Cell Viability inNeuroblastoma Progenitor and Glioblastoma Stem-Like Cells within 15 Daysafter Infection

H-1PV could be shown to induce significant cytopathic effects oncultured neuroblastoma neurospheres. In order to quantify cytopathiceffects with regard to metabolic activity and cellular integrity, MTTtest was performed in NB124 and NCH 421 cells 15 days after infectionwith increasing MOIs of wtH-1PV. Applying an MOI of 1 pfu/cell reducedviable neuroblastoma progenitor cells by 80% and in glioblastomastem-like cells by 60% within 15 days after infection (FIG. 5).

EXAMPLE 7 H-1PV Induces Cytostatic Effects on Neuroblastoma ProgenitorCells and on Three Glioblastoma Stem-like Cell Lines in a Dose-dependentManner

NB 124 neuroblastoma neurosphere cultures and glioblastoma stem-likecells NCH 421, NCH 620 and NCH 644 were infected with either 1 pfu percell (FIG. 6, left panel) or 50 pfu per cell (FIG. 6, right panel) andsubsequently viable cells were counted in multiplicates of 6 wells pertime point. Starting from day 12 to 15 after infection a significantdifference in the number of viable cells could be demonstrated for eachtumor stem cell line. Applying an MOI of 1 the effect was lesspronounced than after application of the higher MOI of 50 p. f. u. percell (FIG. 6; upper curve: mock; lower curve: H-1PV).

EXAMPLE 8 Cytostatic Effect on “Tumor Stem Cells” Does Not Seem to beMediated by Apoptosis

Neuroblastoma and high-grade glioma neurosphere cell cultures wereanalyzed by propidium idodine staining and subsequent flow cytometry forthe presence of a sub-G1 DNA content (less that 2n) cell population thatis indicative of DNA fragmentation and apoptosis. In parallel WesternBlots for the detection of viral proteins such as NS1 were performed.However induction of NS1-expression in NB124 neuroblastoma stem cellsnor in high grade glioma “stem” cells neither correlated with G2-arrestnor with the appearance of a sub-G1 population.

REFERENCES

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The invention claimed is:
 1. A method of combating cancer stem cells(CSCs) in a subject having metastatic cancer disease, comprisingadministering to said subject a composition comprising parvovirus H-1(H-1PV) effective for therapeutically destroying said CSCs which arecharacterized by the expression of stem cell markers CD133, nestin,and/or SOX2.
 2. The method of claim 1, wherein said CSCs are selectedfrom the group consisting of CSCs resistant to chemotherapy orradiotherapy, potentially relapsing CSCs and neuroblastoma stem cells.3. The method of claim 1, wherein said composition is administered byintravenous (i.v.) or intratumoral administration.
 4. The method ofclaim 1, wherein said composition further comprises a pharmaceuticallyacceptable carrier.
 5. A method of combating cancer stem cells (CSCs) ina subject suffering cancer relapse, comprising administering to saidsubject a composition comprising parvovirus H-1 (H-1PV) effective fortherapeutically destroying said CSCs which are characterized by theexpression of stem cell markers CD133, nestin, and/or SOX2.
 6. Themethod of claim 5, wherein said CSCs are selected from the groupconsisting of CSCs resistant to chemotherapy or radiotherapy,potentially relapsing CSCs or neuroblastoma stem cells.
 7. The method ofclaim 5, wherein said composition is administered by intravenous (i.v.)or intratumoral administration.
 8. The method of claim 5, wherein saidcomposition further comprises a pharmaceutically acceptable carrier.